Subject: Irrationals Dense?
From: "William J. Rapaport" <rapaport@buffalo.edu>
Date: Tue, 15 Dec 2009 13:26:46 -0500 (EST)

A student writes:
"Just out of curiosity, is the set of all irrational numbers dense?"

Reply:
Yup! http://en.wikipedia.org/wiki/Dense_set

(PS: It won't be on the test ;-)